In recent years, three-dimensional graphics have been used in various fields. For example, in the scientific field, it is used, e.g., when displaying the results of numerical calculation or when viewing the structure of a protein. In the industrial field, it is used for, e.g., automobile designing, architectural designing, or CAD (Computer Aided Design). Also, for familiar examples, it can be seen in TVs, PCs, video games, etc.
Many systems employ a mouse as an input device for rotating a three-dimensional object displayed on a screen. In most applications, an operation to rotate a three-dimensional object with a mouse enables rotation of the object around the vertical axis on the screen when moving the mouse rightward or leftward and rotation of the object around the horizontal axis when moving the mouse forward or backward.
However, it is impossible to freely rotate the three-dimensional object by means of instinctive mouse operation. In other words, it is not easy to rotate the object around an axis perpendicular to the screen by means of operating the mouse to move back and forth and around. For example, in order to rotate the object around an axis perpendicular to the screen by 180 degrees, it is necessary to, first, move the mouse to the right or left to rotate it around the vertical axis by 180 degrees, and then, to move the mouse forward or backward to rotate it around the horizontal axis by 180 degrees. An operation to perform rotation around an axis perpendicular to the screen may be possible, but when it comes to rotation around an axis slightly diagonally intersecting with the screen, an operation to perform such rotation is extremely difficult.
Japanese Patent Laid-Open No. 2005-32245 describes a controller for a video game. This controller includes a joystick shaft, a spherical element mounted below the joystick shaft, an imager that sequentially inputs images of the surface of the spherical element, and a movement detector that detects movement of the element based on the results of comparison between the plural input images. This controller is basically used as an input device for two-dimensional or three-dimensional coordinates, and is not intended for rotation of a three-dimensional object displayed on a screen.
Japanese Patent Laid-Open No. 2000-330722 describes a position information input device for three-dimensionally moving a displayed image. This input device includes a rotation detecting mechanism for rotating a displayed image around an X-axis, a Y-axis and a Z-axis. The rotation detecting mechanism is configured to, upon a sphere being rolled with the tip of a finger, output the direction and amount of the rotation; however, the detection of the rotation is performed mechanically.
Japanese Patent Laid-Open No. 2000-207093 describes a rotation display device for a three-dimensional figure. This rotation display device, upon a ball body being rotated with a hand, detects such rotation to rotate a displayed image concurrently; however, the detection of the rotation is also performed mechanically.
Japanese Patent Laid-Open No. 9-218744 describes a mouse for rotating a displayed three-dimensional graphic image; however, the structure thereof is completely different from the present invention, which will be described later.